The objective of the proposed research is to determine the mechanisms by which progesterone and estradiol control the cellular differentiation which takes place in the uterine endometrium during early pregnancy. Of the tissue layers of the uterus, primarily the endometrium is involved in the implantation of the blastocyst and in the rapid growth and differentiation characteristic of placental development. In the proposed studies, endometrial cells obtained prior to blastocyst implantation and also during early decidualization will be fractionated by sedimentation at unit gravity before determination of biochemical and morphological characteristics. The hormonal control of DNA, RNA, protein and glucose-6-phosphate dehydrogenase synthesis will be determined in enriched cell populations. Since both blastocyst implantations and endometrial decidualization involve precise hormonal controls of the biochemistry of discrete populations of endometrial cells, a better understanding of these cellular control mechanisms should contribute to our knowledge of significant events of reproductive physiology.